Polycrystalline diamond composite compact element, tools incorporating same and method for making same

ABSTRACT

The invention relates to a PCD composite compact element comprising a PCD structure integrally bonded at an interface to a cemented carbide substrate; the PCD structure comprising coherently bonded diamond grains having a mean size no greater than 15 microns; the cemented carbide substrate comprising carbide particles dispersed in a metallic binder, the carbide particles comprising a carbide compound of a metal; wherein the ratio of the amount of metallic binder to the amount of the metal at points in the substrate deviates from a mean value by at most 20 percent of the mean value. The invention further relates to a method for making a PDC compact element comprising a PCD structure integrally bonded to a substrate formed of cemented carbide; the method including introducing a source of excess carbon to the substrate at a bonding surface of the substrate to form a carburised substrate; contacting an aggregated mass of diamond grains with the carburised substrate; and sintering the diamond grains in the presence of a solvent/catalyst material for diamond; wherein the mean size of the diamond grains in the aggregated mass is no greater than 30 microns.

FIELD

The invention relates to polycrystalline diamond (PCD) compositecompacts comprising a PCD structure bonded to a cemented carbidesubstrate, tools incorporating same and methods for making same.

BACKGROUND

Polycrystalline diamond (PCD) is a super-hard material comprising a massof inter-grown diamond grains and interstices between the diamondgrains. PCD is typically made by subjecting an aggregated mass ofdiamond grains to an ultra-high pressure of at least about 5.5 GPa andtemperature of at least about 1,400 degrees centigrade. As used herein,the term polycrystalline diamond, or PCD, is understood to mean amaterial that comprises at least 80 volume percent of diamond grains, asubstantial portion of which are directly inter-bonded, alternativelyreferred to as coherently bonded. Material wholly or partly filling theinterstices is referred to as filler material. PCD is typically formedin the presence of a sintering aid such as cobalt, which promotes theinter-growth of diamond grains. The sintering aid is commonly referredto as a solvent/catalyst material for diamond, owing to its function ofdissolving diamond to some extent and catalysing its re-precipitation. Asolvent/catalyst material for diamond is understood to be a materialcapable of promoting the growth of diamond and the formation of directdiamond-to-diamond bonds at a temperature and pressure at which diamondis thermodynamically stable. Generally preferred solvent/catalystmaterials are Fe, Ni, Co and Mn, and alloys including any of these.Consequently the interstices within the sintered PCD product are whollyor partially filled with residual solvent/catalyst material. Typically,PCD is often formed on a cobalt-cemented tungsten carbide substrate,which provides a source of cobalt solvent/catalyst for the PCD.

PCD is used in a wide variety of tools for cutting, machining, drillingor degrading hard or abrasive materials such as rock, metal, ceramics,composites and wood-containing materials. For example, PCD inserts arewidely used within drill bits used for boring into the earth in the oiland gas drilling industry. In many of these applications the temperatureof the PCD material becomes elevated as it engages a rock formation,workpiece or body with high energy. Unfortunately, mechanical propertiesof PCD such as hardness and strength tend to deteriorate at hightemperatures, largely as a result of residual solvent/catalyst materialdispersed within it.

U.S. Pat. No. 4,694,914 discloses an insert including at least one outerlayer containing polycrystalline diamond and at least one transitionlayer between the polycrystalline diamond layer and the cemented carbidebody. The transition layer comprises a composite material containingdiamond crystals, cobalt and pre-cemented tungsten carbide particles.

U.S. Pat. No. 4,694,918 discloses inserts including a cemented metalcarbide insert body, an outer layer of polycrystalline diamond, and atleast one transition layer of a composite material. The compositematerial includes polycrystalline diamond and particles of pre-cementedmetal carbide.

Delwiche et al. (Petroleum Division, v 40, and Drilling Technology 1992,1992, p 51-60, American Society of Mechanical Engineers) disclose PCDinserts for oil and gas drilling, wherein a PCD layer is secured to asubstrate comprising a back-up component containing coarse diamondgrains dispersed within a matrix of cemented carbide.

There is a need to provide composite PCD compacts comprising a PCDstructure, and particularly a PCD structure formed from fine orultra-fine grains of diamond, bonded to a cemented carbide substrate andhaving reduced defects proximate the interface between the PCD structureand the cemented carbide substrate.

SUMMARY

According to a first aspect of the invention there is provided a PCDcomposite compact element comprising a PCD structure integrally bondedat an interface to a cemented carbide substrate; the PCD structurecomprising coherently bonded diamond grains having a mean size nogreater than about 30 microns, preferably no greater than about 20microns, more preferably no greater than about 15 microns, even morepreferably no greater than about 10 microns, yet more preferably nogreater than about 5 microns, still more preferably no greater thanabout 2 microns, and even more preferably no greater than about 1micron; the cemented carbide substrate comprising carbide particlesdispersed in a metallic binder, the carbide particles comprising acarbide compound of a metal; wherein the ratio of the amount of metallicbinder to the amount of the metal at points in the substrate deviatesfrom a mean value by at most about 20 percent of the mean value.

In one embodiment the ratio of the amount of metallic binder to theamount of the metal at points in the substrate deviates from a meanvalue by at most about 20 percent of the mean value from the interfaceto a depth of at least 2 mm into the substrate.

Embodiments of this aspect of the invention have been found to exhibitreduced exaggerated grain growth proximate the interface between the PCDstructure and the substrate, and are believed to be even moreadvantageous the lower the mean diamond grain size within the PCDstructure.

In one embodiment of this apsect to the invention, the ratio of theamount of metallic binder to the amount of the metal at points in thesubstrate deviates from the mean value by at most about 10 percent ofthe mean value.

In some embodiments, the mean size of the diamond grains may be at leastabout 0.05 microns or at least about 0.1 microns.

In some embodiments the metal of the carbide particles may be arefractory metal such as W, or even Ti, Ta, or Cr, and in someembodiments the metallic binder comprises a solvent/catalyst fordiamond, such as Co.

In some embodiments diamond particles are dispersed within a surfaceregion of the substrate or substantially throughout the entiresubstrate. In some embodiments, the content of the diamond particleswithin the surface region or within the substrate may be no greater thanabout 6 weight percent or no greater than about 5.5 weight percent ofthe material in the surface region or in the substrate as the case maybe. In some embodiments, the content of the diamond particles within thesurface region or within the substrate may be at least about 0.1 weightpercent or at least about 0.3 weight percent. The surface region of thesubstrate may extend from the interface to a depth of at least about 1mm, at least about 2 mm, or even at least 3 mm. In some embodiments, thesurface region extends from the interface and has a volume of at least 2times that of the PCD structure or at least 3 times that of the PCDstructure. In some embodiments the volume of the surface regionextending from the interface may be at least ten times greater than thevolume of the PCD structure.

In some embodiments, the diamond particles dispersed in the substrate orin the surface region of the substrate have mean size in the range from0.1 to 100 microns, 0.1 to 50 microns or even 0.1 to 20 microns. In someembodiments the diamond particles may be substantially uniformlydispersed throughout the substrate or the surface region of thesubstrate. This may help reduce the occurrence of grain growth-relateddefects more uniformly over the interfacial area.

In some embodiments, the diamond content within the substrate or withinthe surface region of the substrate may be at least 1 volume percent, atleast 2 volume percent and less than 20 volume percent, in the rangefrom 1 to 15 volume percent, or in the range from 1 to 10 volumepercent. It has been found that diamond content within these ranges maybe sufficient to substantially reduce certain defects proximate theinterface.

In some embodiments the PCD structure comprises a first and a secondregion, the mean size of the diamond grains of the first region beinggreater than that of the diamond grains in the second region; the firstregion being proximate the substrate and the second region being remotefrom the substrate. In one embodiment the second region defines aworking surface. In some embodiments, the mean size of the diamondgrains in the first region of the PCD structure may be greater than 2microns and the mean size of the diamond grains in the second region ofthe PCD structure may be in the range from 0.01 micron to 1.5 microns orin the range from 0.01 micron to 1 micron. These embodiments may havesubstantially reduced incidence of grain growth defects proximate theinterface between the PCD structure and the substrate in the case ofvery fine-grained PCD structures. Very fine-grained (less than about 2microns) PCD structures may be desirable because they have certaindesirable mechanical properties, such as increased toughness. The PCDstructure may have an axial thickness of at least 1 mm from an interfacewith the substrate.

The ratio of the amount of metallic binder to the amount of carbon atpoints in the PCD structure may be substantially constant about a meanvalue, from the interface to a depth of at least 0.5 mm, more preferablyat least 0.75 mm and yet more preferably at least 1 mm into the PCDstructure. In one embodiment, the ratio of the amount of metallic binderto the amount of carbon at points in the PCD structure deviates from themean value by at most 20 percent of the mean value, more preferably atmost about 10 percent from the mean value.

The substrate may have a thickness of at least 1 mm, at least 1.5 mm orat least 5 mm.

The diamond grains in PCD structure may have a multi-modal sizedistribution. In some embodiments the bonded diamond grains of the PCDstructure have the size distribution characteristic that at least 50percent of the grains have mean size greater than 5 microns, and atleast 20 percent of the grains have mean size in the range from 10 to 15microns. Embodiments of PCD structures having a multi-modal diamondgrain size distribution and mean grain size within these ranges havebeen found to have sufficient strength to retain better their mechanicalintegrity and key properties after bonding to the substrate, such as bybrazing.

In one embodiment a plurality of PCD or diamond-rich fingers extend fromthe PCD structure into the substrate, more preferably a plurality of PCDfingers extend from the PCD structure into the substrate, a finger beinga generally elongate structure. In some embodiments, at least one of thePCD fingers has length at least 20 microns, at least 30 microns, or atleast 40 microns.

Embodiments of a PCD composite compact element according to theinvention may be made using an embodiment of the method according to anaspect of the invention.

Excess carbon is understood to be carbon that is in excess of thediamond of the diamond grains provided in the aggregated mass forsintering PCD, and is also in excess of the carbon included as thecarbide of the cemented carbide (stochiometric excess). A carburisedsubstrate or carburised substrate assembly is therefore a substrate orsubstrate assembly including excess carbon.

A green body is a term known in the art and refers to an articleintended to be sintered, but which has not yet been sintered. It isgenerally self-supporting and has the general form of the intendedfinished article. A green body is typically formed by combining aplurality of particles in a vessel and then compacting them to formself-supporting article.

Carbon may be introduced into the substrate in any of a number of ways.In one embodiment a substrate pre-form is prepared by a method includingintroducing diamond particles into the starting powders for making acemented carbide to form a starting powder blend; forming the startingpowder blend by means of compaction in a mould to form a green body; andsintering the green body at a temperature of greater than about 1,400degrees centigrade at an applied pressure of less than about 1 GPa toproduce a sintered substrate. At least some of the diamond particles areconverted wholly or partially into graphite during this carbidesintering step, because the pressure is below that for diamond to bethermodynamically stable.

The sintering pressure at which diamond is thermodynamically stable ispreferably at least about 5.5 GPa and the temperature is preferably atleast about 1,400 degrees centigrade.

In some embodiments, carbon is introduced into the substrate in the formof graphite powder.

In some embodiments, carbon is introduced into the substrate in the formof carbonaceous gas, which is caused to permeate or infiltrate thesubstrate.

In some embodiments, material comprising carbon is sprayed onto asurface of the substrate. In particular, powder containing cobalt,carbon and tungsten may be deposited onto the substrate surface by meansof thermal spraying.

In some embodiments, the substrate is coated with a source of excesscarbon, such as graphite.

In some embodiments, the substrate is prepared from starting carbidepowder having a high content of carbon in the form of carbon black, forexample.

In some embodiments, a substrate with high carbon content is prepared byavoiding the removal of some carbon during the preparation of the greenbody for readiness for sintering. Typically, a green body is heattreated to remove binder or pressing aid material prior to sintering,and carbon is removed during this process. In one embodiment, thisprocess is not thoroughly completed, leaving at least some carbon ofbinder origin within the green body.

The size distribution of unbonded or free-flowing diamond grains ismeasured by means of a laser diffraction method, wherein the grains aresuspended in a fluid medium and an optical diffraction pattern isobtained by directing a laser beam at the suspension. The diffractionpattern is interpreted by computer software and the size distribution isexpressed in terms of equivalent circle diameter. In effect, the grainsare treated as being spherical and the size distribution is expressed interms of a distribution of equivalent diameters of spheres. AMastersizer™ apparatus from Malvern Instruments Ltd, United Kingdom, maybe used for his purpose.

A multi-modal size distribution of a mass of grains is understood tomean that the grains have a size distribution that is formed of morethan one peak, each peak corresponding to a respective “mode”.Multimodal polycrystalline bodies are typically made by providing morethan one source of a plurality of grains, each source comprising grainshaving a substantially different mean size, and blending together thegrains from the sources. Measurement of the size distribution of theblended grains typically reveals distinct peaks corresponding todistinct modes. When the grains are sintered together to form thepolycrystalline body, their size distribution is further altered as thegrains are compacted against one another and fractured, resulting in theoverall decrease in the sizes of the grains. Nevertheless, themultimodality of the grains is usually still clearly evident from imageanalysis of the sintered article.

In order to obtain a measure of the sizes of diamond grains within PCD,a method known as “equivalent circle diameter” is used. In this method,a scanning electron micrograph (SEM) image of a polished surface of thePCD material is used. The magnification and contrast should besufficient for at least several hundred diamond grains to be identifiedwithin the image. The diamond grains can be distinguished from metallicphases in the image a circle equivalent in size for each individualdiamond grain can be determined by means of conventional image analysissoftware. The collected distribution of these circles is then evaluatedstatistically. Wherever diamond mean grain size within PCD material isreferred to herein, it is understood that this refers to the meanequivalent circle diameter.

“Binder pooling” refers to the existence of a region within the PCDstructure adjacent the interface, the region having a substantiallyhigher content of binder material (typically cobalt) than the mean ordesired content within the PCD structure. The diamond content within thepooling region may be less than 50% in known PCD compacts, particularlythose having a cemented carbide substrate thicker than about 1millimetre and a PCD structure having thickness greater than about 0.6millimetres. Pooling is a problem particularly in PCD compacts havingrelatively thick substrate and PCD structure. A corresponding regionoccurs within the substrate adjacent the interface, wherein the contentof binder material is lower than the mean for the substrate. This issometimes called a “binder denuded zone”. Binder pooling and depletionmay be undesirable because it is associated with several relateddefects, including so-called “plume” defects and exaggerated diamondgrain growth, and because it reduces the abrasion resistance of thecompact in a region adjacent the interface. Reduced abrasion resistanceat the interface may result in under-cutting of the PCD structure, whichmay be accelerated by the presence of erosion-promoting material in theenvironment.

Plume defects are relatively large grains of metal carbide formed withinthe PCD structure proximate the interface. While wanting not to be boundby theory, it is believed that plumes may be reduced in embodiments ofthe invention because material infiltrating from the substrate into thePCD during the sintering step has reduced tungsten content or issubstantially free of tungsten.

Embodiments of the method of the invention may also result in reducedexaggerated grain growth of diamond within the PCD, which is more aproblem the finer the diamond grains starting aggregated mass. For thisreason the method is particularly advantageous where the mean grain sizewithin the PCD is low. While wanting not to be bound by theory, whenplumes of molten binder material, e.g. cobalt, invade the diamond layerand the plumes have a relatively low content of carbon, fine diamondgrains readily dissolve and re-precipitate onto the larger grains,resulting in exaggerated grain diamond grain growth proximate theinterface between the PCD structure and the substrate. The resultinggrains can be an order of magnitude greater than the starting grainsize. However, when the binder material contains relatively more carbon,as is the case where the source of excess carbon has been introducedinto the substrate prior to the sintering step, then dissolution offiner grains is suppressed or retarded and instead, the carbonprecipitates evenly onto all grains. Since this precipitation is spreadout over many grains, there is little or reduced exaggerated graingrowth.

Substantially constant is understood to mean that the ratio is aconstant value with a statistical confidence interval of at least 68percent, or even 90 or 95 percent.

The ratio of the amount of binder material in the substrate to theamount of carbide material within the substrate, and the ratio of amountof binder material to the amount of diamond within the PCD structure maybe expressed as a weight ratio, volume ratio or other ratio indicativeof the relative amounts of binder material and carbide material, or ofbinder material and diamond, respectively. The ratio may be expressed asa percentage value.

Where the substrate contains diamond particles in a region adjacent theinterface with the PCD structure, it has been found that a type of“reverse pluming” occurs, where PCD “fingers” extend from the PCDstructure into the region. It is hypothesised that these fingers mayresult in reduced internal stress proximate the interface and reducedincidence of delamination of the structure. The size of the fingers maybe controlled by selecting the size of the diamond particles introducedinto the substrate green body; the longer the fingers desired, thelarger should be the diamond particles, in general. The number offingers and to some extent their size is controlled by the number ofdiamond particles introduced into the substrate.

According to a second aspect to the present invention there is provideda method for making a polycrystalline diamond composite (PDC) compactelement comprising a polycrystalline diamond (PCD) structure integrallybonded to a substrate formed of cemented carbide; the method includingintroducing a source of excess carbon to the substrate at or proximate abonding surface of the substrate to form a carburised substrate orcarburised substrate assembly; contacting an aggregated mass of diamondgrains with the carburised substrate or carburised substrate assemblyadjacent or proximate the bonding surface to form an unbonded assembly;and sintering the diamond grains in the presence of a solvent/catalystmaterial for diamond at a temperature and pressure at which diamond isthermodynamically stable to form PCD; wherein the mean size of thediamond grains in the aggregated mass is no greater than about 30microns.

The mean size of the diamond grains in the aggregated mass may be nogreater than about 20 microns, preferably no greater than about 15microns, even more preferably no greater than about 10 microns, yet morepreferably no greater than about 5 microns, still more preferably nogreater than about 2 microns and even more preferably no greater thanabout 1 micron. Preferably, the mean size of the diamond grains in theaggregated mass is at least about 0.05 microns, more preferably at leastabout 0.1 microns.

Embodiments of the invention have been found to reduce exaggerated graingrowth proximate the bonding surface, and may be even more advantageousthe lower the mean diamond grain size.

In one embodiment, the method includes forming a carburised substrate,wherein source of excess carbon is included in or introduced into thevolume of the substrate. In some embodiments the source of excess carbonis dispersed substantially throughout the entire volume of thecarburised substrate. In other embodiments the source of excess carbonis dispersed in a surface region proximate or adjacent the bondingsurface.

Preferably, the mean content of the source of excess carbon within asurface region of the carburised substrate or throughout substantiallythe entire carburised substrate is no greater than about 10 weightpercent, more preferably no greater than about 6 weight percent and yetmore preferably no greater than about 5.5 weight percent of the materialin the surface region or the substrate. Preferably, the content of thesource of excess carbon within the surface region or throughout theentire carburised substrate is at least about 0.1 weight percent andmore preferably at least about 0.3 weight percent of the material in theregion. In some embodiments the surface region extends to a depth of atleast about 1 mm, at least about 2 mm, or even at least 3 mm from thebonding surface. In some embodiments, the surface region has a volume ofat least 2 times that of the PCD structure or at least 3 times that ofthe PCD structure. In some embodiments the volume of the surface regionmay be at least ten times greater than the volume of the PCD structure.

The weight percent is expressed of the total substrate material withinthe region in which the carbon is introduced

In one embodiment the diamond grains in the aggregated mass have amulti-modal size distribution.

Preferably, the source of excess carbon is a carbonaceous material otherthan metal carbide, such as carbon black powder or graphite. In oneembodiment the source of excess carbon may be derived from diamond thathas been converted into a non-diamond material. Such materials mayconsist essentially of carbon and may not substantially introduceunwanted material into the substrate or PCD. In some embodiments thesource of excess carbon may be in the form of organic molecules. In someembodiments the source of excess carbon may be introduced in the form ofa gas, such as a gas of organic molecules such as methane.

In one embodiment, the method includes combining source of excess carbonin particulate or granular form with raw materials for the cementedcarbide, forming the combination into a substantially self-supportinggreen body, and sintering the green body at a pressure at which diamondis not thermodynamically stable to form the carburised substrate. Insome embodiments the raw materials for cemented carbide comprise grainsof tungsten carbide and grains comprising cobalt.

The method may include combining diamond grains with raw materials forcemented carbide, forming the combination into a substantiallyself-supporting green body; subjecting the green body to a temperatureof at least 500 degrees centigrade and a pressure at which diamond isnot thermodynamically stable to form the carburised substrate. Thediamond particles may be wholly or partly converted into a non-diamondmaterial, particularly graphite. In one embodiment, substantially all ofthe converted diamond re-converts to diamond during the step ofsintering the PCD. This embodiment has been found to result in PCDfingers extending into the substrate, which may result in improvedbonding of the PCD to the substrate and reduced incidence ofdelamination.

In one embodiment of this aspect to the invention, the substrate issubstantially free of diamond.

In embodiments where the substrate includes diamond particles formedfrom converted graphite, for example where the source of excess carbonis graphite, the diamond particles may have little or substantially noplastic deformation within at least a peripheral volume of each diamondparticle. In some embodiments the diamond particles have substantiallyno plastic deformation.

In some embodiments, the source of excess carbon may be deposited onto abonding surface of the substrate to form a carburised substrate orcarburised substrate assembly. In some embodiments the source of excesscarbon may be deposited onto the substrate bonding surface by means of athermal or other spraying method. In one embodiment a disc or filmcomprising a refractory metal, such as tungsten may be placed over thedeposited source of excess carbon to form a carburised substrateassembly.

The method may include introducing metal carbide or a precursor orprecursors for metal carbide into the aggregated mass of diamond grains.More preferably, the method includes introducing refractory metalcarbide particles, for example tungsten carbide, tantalum carbide,niobium carbide or vanadium carbide, into the aggregated mass of diamondgrains. In some embodiments the method includes introducing a refractorymetal precursor for metal carbide, for example tungsten, tantalum,niobium or vanadium in non-carbide compound or in elemental form, intothe aggregated mass of diamond grains. In embodiments of the methodwhere a source of excess carbon may be introduced to or into thesubstrate, the introduction of metal carbide into the aggregated mass ofdiamond grains, directly or via the introduction of precursor orprecursors, may significantly enhance the abrasion or erosion resistanceof the sintered PCD structure.

In some embodiments the metal carbide or a precursor or precursors formetal carbide may be introduced in particulate form into the aggregatedmass of diamond grains by blending the particles with the diamondgrains.

In some embodiments the cemented carbide comprises grains of metalcarbide cemented together by a metal binder, the metal binder comprisinga solvent/catalyst material for diamond, such as cobalt. Such metalbinder may infiltrate the aggregated mass of diamond particles duringthe sintering step and function as a sintering aid for diamond.

Embodiments of the invention have been found to reduce or eliminatepooling of the metal binder material within the PCD adjacent theinterface with the substrate and the corresponding depletion of metalbinder material within the substrate adjacent the bondingsurface/interface, and may reduce or eliminate certain defectsassociated with carbide or diamond grain growth proximate the bondingsurface.

According to a third aspect of the invention there is provided a PCDcutter insert for a drill bit, such as a drill bit for boring into theearth, the PCD cutter insert comprising a PCD composite compact elementaccording to the invention.

According to a fourth aspect of the invention there is provided a drillbit for boring into the earth, the drill bit comprising a PCD cutterinsert according to the invention.

Boring into the earth as carried out in the oil and gas drillingindustry exerts high forces on a cutter insert and PCD cutter insertsaccording to the invention may exhibit reduced failure rate in use.

DRAWING CAPTIONS

Non-limiting embodiments will now be described with reference to theaccompanying drawings of which:

FIG. 1 shows (a) a schematic drawing of a perspective view of anembodiment of a PCD composite compact element, as well as longitudinalside cross-sectional views of two embodiments, (b) and (c).

FIGS. 2 to 7 are schematic drawings of perspective views of embodimentsof PCD composite compact elements.

FIG. 8 shows a graph of number of grains versus equivalent circlediameter grain size for a fine-grained bi-modal size distribution ofdiamond grains within an embodiment of PCD material.

FIG. 9 shows a graph of number of grains versus equivalent circlediameter grain size for diamond grains within an embodiment of PCDmaterial.

FIG. 10 shows a schematic graph of binder content as well as the carboncontent in the PCD and the substrate as a function of depth from the PCDworking surface in the case of a prior art PCD composite compact as wellas in the case of an embodiment of the invention.

FIG. 11 is a graph showing the ratio of cobalt to tungsten content as afunction of distance into the substrate from the interface with the PCDstructure, in the case of an embodiment of the invention (data shown asfilled squares) and a control according to the prior art (data shown asunfilled diamonds).

FIG. 12 is a graph showing the ratio of cobalt to carbon content as afunction of distance into the PCD structure from the interface with thesubstrate, in the case of an embodiment of the invention (data shown asfilled squares) and a control according to the prior art (data shown asunfilled diamonds).

FIG. 13 shows a scanning electron micrograph of a cross-section of abonding interface between a PCD structure and a cobalt-cemented WCsubstrate enhanced with diamond.

DETAILED DESCRIPTION OF EMBODIMENTS

With reference to FIG. 1, an embodiment of a polycrystalline diamondcomposite compact (PCD) element, 100, comprises a PCD structure, 110,integrally bonded to a cemented carbide substrate, 120, at an interface,125. In some embodiments the interface between the embodiment shown in(a) The PCD structure, 110, has an axial thickness t_(PCD) and thesubstrate, 120, has an axial thickness t_(sub), the axial thicknessbeing measured from an interface, 125, between the PCD structure, 110,in an axial direction indicated by the line marked “axial”. In anembodiment shown in (b), the interface, 125, is substantially planar,and in an embodiment shown in (c), the interface, 125, is non-planar andthe PCD structure, 110, has at least two thicknesses, t_(PCD-1) andt_(PCD-2).

With reference to FIG. 2, an embodiment of a polycrystalline diamondcomposite compact (PCD) element, 100, comprises a PCD structure, 110,integrally bonded to a cemented carbide substrate, 120, at an interface,125, and the PCD structure comprises a first region, 112, and a secondregion, 111, the mean size of the diamond grains of the first region,112, being greater than that of the diamond grains in the second region,111; the first region, 112, being proximate the substrate, 120, and thesecond region, 111, being remote from the substrate, 120.

With reference to FIG. 3, an embodiment of a polycrystalline diamondcomposite compact (PCD) element, 100, comprises a PCD structure, 110,integrally bonded to a cemented carbide substrate, 120, at an interface,125, wherein the substrate, 120, includes diamond particles dispersedwithin a surface region, 221, extending from the interface to a depth.The remaining region, 122, of the substrate, 120, is substantially freeof diamond. In some embodiments the depth is at least 1 millimetre, atleast 2 millimetres or at least 3 millimetres. In some embodiments thesurface region, 121, of the substrate has a volume of at least 2 timesthat of the PCD structure, 110, at least 3 times that of the PCDstructure, 110, or even at least ten times greater than the volume ofthe PCD structure, 110.

With reference to FIG. 4, an embodiment of the method of the inventionincludes introducing a source of excess carbon to the substrate, 220, ator proximate a bonding surface, 225, to form a carburised substrateassembly, 250; contacting an aggregated mass, 210, of diamond grainswith the carburised substrate assembly, 250, adjacent or proximate thebonding surface, 225, to form an unbonded assembly, 200; wherein thesource of excess carbon is in the form of graphite dispersed in asurface region, 221, of the substrate, 220, the surface region extendingfrom proximate the bonding surface, 125, to a depth. In some embodimentsthe depth is at least 1 millimetre, at least 2 millimetres or at least 3millimetres. With reference to FIG. 5, the source of excess carbon is inthe form of graphite dispersed substantially throughout the entirevolume of the substrate, 220.

With reference to FIG. 6, an embodiment of the method of the inventionincludes introducing a source of excess carbon to the substrate, 220, ator proximate a bonding surface, 225, to form a carburised substrateassembly, 250; contacting an aggregated mass, 210, of diamond grainswith the carburised substrate assembly, 250, adjacent or proximate thebonding surface, 225, to form an unbonded assembly, 200; wherein thesource of excess carbon, 230, is deposited onto a bonding surface, 125,of the substrate. With reference to FIG. 7, an embodiment of the methodof the invention includes placing a disc or film, 240, comprisingtungsten over the deposited source of excess carbon, 230.

For example, FIG. 8 shows a graph of number of grains versus equivalentcircle diameter grain size for a fine-grained bi-modal size distributionof diamond grains within an embodiment of PCD material; and FIG. 9 showsa graph of number of grains versus equivalent circle diameter grain sizefor diamond grains within an embodiment of a multi-modal PCD material.

The PCD material having the diamond grain size distribution shown inFIG. 8 is an example of an embodiment of PCD material that may benefitparticularly well from the invention, wherein the mean size of thediamond grains within the sintered PCD is in the range from about 1.5 toabout 6 microns and the size distribution can be resolved into at leasttwo distinct peaks. FIG. 8 shows the distribution of equivalent circlediameters, with no Saltykov correction having been applied to convertthe size distribution obtained from the two-dimensional image data to agrain size distribution in three dimensions.

With reference to FIG. 9, the relative (e.g. weight percent) content ofcobalt, 200, within a prior art PCD composite compact, 210, and a PCDcomposite compact according to an embodiment of the invention, 220, arecompared in respect of qualitative features. In some embodiments of theinvention binder pooling is substantially reduced. In some embodimentsthe incidence of plume defects is substantially reduced. Also shown inFIG. 9 are the corresponding relative content of carbon, 400, within aprior art PCD composite compact, 410, and a PCD composite compactaccording to an embodiment of the invention, 420, are compared inrespect of qualitative features. The region of the graphs indicated by110 corresponds to the PCD structure and the region indicated by 121corresponds to the carbide substrate.

FIG. 10 is a graph showing the ratio of cobalt to tungsten as a functionof axial distance into the substrate from the interface with the PCDstructure, in the case of an embodiment of the invention (data shown asfilled squares) and a control according to the prior art (data shown asunfilled diamonds). The interface corresponds to zero millimetres. In anembodiment of the invention, the ratio (shown as filled squares) remainssubstantially constant from the interface into the bulk of thesubstrate, the standard deviation of the data being less than about 5percent of the mean value, M. The upper and lower standard deviationsare indicated as SU and SL, respectively. The upper and lower percentlimits or M(1+20%) and M(1−20%), are shown as LU and LL, respectively.In the case of a control material, made according to the prior art, themean ratio of cobalt to tungsten is substantially lower within a depthof approximately 1.5 millimetres is substantially and systematicallyless than the mean value in the bulk of the substrate, and is less thanthe lower limit M(1−20%) within a depth of about 1 millimetre from theinterface. This is called the “depleted zone”.

FIG. 11 is a graph showing the ratio of cobalt to carbon as a functionof axial distance into the PCD structure from the interface with thesubstrate, in the case of an embodiment of the invention (data shown asfilled squares) and a control according to the prior art (data shown asunfilled diamonds). The interface corresponds to zero millimetres. In anembodiment of the invention, the ratio (shown as filled squares) remainssubstantially constant from the interface into the bulk of the PCDstructure, even within the first 0.2 millimetres from the interface,where the ratio in the control material increases dramatically togreater than M(1+20%), corresponding to binder pooling within the PCDstructure adjacent the interface.

With reference to FIG. 12, an SEM micrograph of the region straddling aninterface between a PCD structure, 40, and a cemented carbide substrate,50, of a PCD composite compact according to an embodiment of theinvention is shown. The substrate, 50, contains particles of diamond,46. A “finger”, 45, comprising contiguous polycrystalline diamond andhaving a length in the range of about 30 to 50 microns extends from thePCD structure, 40, into the substrate, 50.

As previously noted, embodiments of the invention may compriserelatively thick PCD caps and substrates without the need for usinghigher temperatures in the sintering step. In general, the thicker thePCD layer, the higher must be the sintering temperature in order to urgemolten solvent/catalyst material from the substrate to infiltrate theentire PCD layer. A serious consequence of this not occurring is thepresence of “soft spot” defects wherein the diamond grains remote fromthe interface have not adequately sintered. Unfortunately, highersintering temperatures result in excessive dissolution of diamondproximate the interface and may result in plume defects in the form ofexaggerated large acicular metal carbide grains. On the other hand,higher sintering temperatures tend to promote exaggerated diamond graingrowth, which is also undesirable. This is less of a problem where thePCD structure is relatively thin, since the minimum sinteringtemperature for the avoidance of soft spots is lower the thinner the PCDstructure. However, many applications require that the PCD structure isseveral millimetres thick and that the substrate is tens of millimetresthick. In particular, PCD compacts used for boring into earth and rockin the oil and gas industry comprise relatively thick PCD caps andsubstrates.

The invention will now be described with reference to the followingnon-limiting examples.

Example 1

A first substrate element for use as the surface region of a substratefor a PCD compact was manufactured by blending together diamondparticles, tungsten carbide (WC) powder and cobalt powder, forming theblended mixture into a compacted green body, and subjecting the greenbody to a conventional carbide sintering process. The diamond particleshad mean size in the range of 0.75 to 1.5 microns, and constituted 3weight percent of the blended mixture. The WC powder and the cobaltpowder had been pre-mixed, the cobalt constituting 13 weight percent ofthe WC—Co pre-mix and the WC particles having a mean size in the rangefrom about 1 to 4 microns. About 2 weight percent organic pressing aidwas included in the WC—Co mix. The blended powder mix was uniaxiallycompacted at ambient temperature to form a substantially cylindricalgreen body, which was conventionally sintered at a temperature of 1,400degrees centigrade for 2 hours to form a sintered article. By the end ofthe sintering process, the diamond particles had completely convertedinto graphite. The substrate had a diameter of about 17.4 millimetresand a height of about 6 millimetres after final machining.

A second substrate element for use as a region of a substratesubstantially free of diamond was manufactured in the same way and usingthe same raw materials as the first substrate element, except that nodiamond was introduced and the height of the second substrate elementwas about 7 millimetres.

The first substrate element was placed on top of the second substrateelement, the first and second substrate elements being substantially inregistration, to form a substrate assembly, having an upper surfacebeing the exposed end surface of the first substrate element.

A layer comprising an unbonded aggregated mass of diamond grains wasdeposited onto the upper surface of the substrate assembly end surfaceof the sintered article to form an unbonded assembly. The diamond grainshad mean size of about 0.5 microns and were coated with cobalt, whichconstituted 5 weight percent of the aggregated mass. The coated grainswere then subjected to heat treatment in a hydrogen rich atmosphere at850 degrees centigrade in order to terminate the surfaces with hydrogen.

The unbonded assembly was mounted within a capsule for an ultra-highpressure furnace, as is known in the art. The capsule was subjected to apressure of about 5.5 GPa and a temperature of about 1,400 degreescentigrade for a period of about 5 minutes. After sintering, the firstand second substrate elements had sintered together and the PCDcomposite compact was processed in the usual way to form an inserthaving a diameter of about 15.9 millimetres and a PCD structure withthickness in the range of about 1.7 to 2.1 millimetres.

The insert was analysed using scanning electron micrography (SEM).Particularly noteworthy was the absence of discernable “pooling” ofcobalt binder adjacent the interface between the PCD and the substrate,which is a typical feature of known inserts, especially those havingrelatively thick PCD and substrate, of which the insert was an example.The sample displayed an abrupt transition between the cemented carbideof the substrate and the PCD. In addition, no substantial exaggerateddiamond or WC grains were observed within the PCD layer proximate theinterface, as occur in known inserts.

Example 2

A substrate a PCD compact was manufactured by blending together diamondparticles, tungsten carbide (WC) powder and cobalt powder, forming theblended mixture into a compacted green body, and subjecting the greenbody to a conventional carbide sintering process. The diamond particleshad mean size of about 22 microns and constituted about 5.8 weightpercent of the blended mixture. The WC powder and the cobalt powder hadbeen pre-mixed, the cobalt constituting 13 weight percent of the WC—Copre-mix and the WC particles having a mean size in the range from about1 to 4 microns. About 2 weight percent organic pressing aid was includedin the WC—Co mix. The blended powder mix was uniaxially compacted atambient temperature to form a substantially cylindrical green body,which was conventionally, sintered at a temperature of 1,400 degreescentigrade for 2 hours to form a sintered article. By the end of thesintering process, the diamond particles had completely converted intographite. The substrate had a diameter of about 17.4 millimetres and aheight of about 13 millimetres after final machining.

A layer comprising an unbonded aggregated mass of diamond grains wasdeposited onto the upper surface of the substrate of the sinteredarticle to form an unbonded assembly. Raw material diamond powder forthe aggregated mass was prepared by blending diamond grains from threesources, each source having a different average grain size distribution.

The unbonded assembly was mounted within a capsule for an ultra-highpressure furnace, as is known in the art. The capsule was subjected to apressure of about 5.5 GPa and a temperature of about 1,400 degreescentigrade for a period of about 5 minutes. After sintering, the firstand second substrate elements had sintered together and the PCDcomposite compact element was processed in the usual way to form aninsert having a diameter of about 15.9 millimetres and a PCD structurewith thickness in the range of about 1.7 to 2.1 millimetres.

The insert was analysed using scanning electron micrography (SEM). TheAnalysis of the material was carried out at several points on a polishedcross-section longitudinally through the interface between the PCDstructure and the substrate. The contents of tungsten (W) and cobalt(Co) were measured within the substrate at several different points fromproximate the interface into the bulk of the substrate, and the contentsof carbon (C) and cobalt (Co) were measured within the PCD structure atseveral different points from proximate the interface into the bulk ofthe PCD structure. The results of these measurements are shown as ratiosas functions of distance from the interface in FIGS. 11 and 12,respectively. Particularly noteworthy was the absence of substantial“pooling” of cobalt binder adjacent the interface between the PCD andthe substrate, which is a typical feature of known inserts, especiallythose having relatively thick PCD and substrate. The sample displayed anabrupt compositional transition between the cemented carbide of thesubstrate and the PCD. In addition, substantially no exaggerated diamondor WC grains were observed within the PCD layer proximate the interface,as occur in known inserts.

Example 3

A substrate a PCD compact was manufactured as in example 2, except thatthe diamond particles had mean size of about 2 microns and constitutedabout 2.7 weight percent of the blended mixture. A layer comprising anunbonded aggregated mass of diamond grains as described in example 2 wasdeposited onto the upper surface of the substrate of the sinteredarticle to form an unbonded assembly, which was sintered as in example 2to form a PCD composite compact element.

As in example 2, the absence of substantial “pooling” of cobalt binderadjacent the interface between the PCD and the substrate was observed,and substantially no exaggerated diamond or WC grains were observedwithin the PCD layer proximate the interface.

Example 4

A substrate for a PCD compact was manufactured in the same way and usingthe same raw materials as the first substrate element of example 1,except that the height of the substrate was 13 millimetres. In otherwords, the whole substrate had substantially the same composition, shapeand diameter as the first substrate element described in example 1.

A layer of unbonded aggregated mass of diamond grains was deposited ontoan end surface of the substrate to form an unbonded assembly. Thediamond grains had an ultra-fine bi-modal distribution, having a meansize in the range from about 0.1 to 1 micrometre and were coated withcobalt, which constituted 5 weight percent of the aggregated mass. Thecoated grains were then subjected to heat treatment in a hydrogen richatmosphere at 850 degrees centigrade in order to terminate the surfaceswith hydrogen.

The unbonded assembly was mounted within a capsule for an ultra-highpressure furnace, as is known in the art. The capsule was subjected to apressure of about 5.5 GPa and a temperature of about 1,400 degreescentigrade for a period of about 5 minutes. After sintering, the PCDcomposite compact was processed in the usual way to form an inserthaving a diameter of about 15.9 millimetres and a PCD structure withthickness in the range of about 1.7 to 2.1 millimetres.

The insert was analysed using scanning electron micrography (SEM).Particularly noteworthy was the absence of discernable pooling of cobaltbinder adjacent the interface between the PCD and the substrate. Thesample displayed an abrupt transition between the cemented carbide ofthe substrate and the PCD. In addition, no substantial exaggerateddiamond or WC grains were observed within the PCD layer proximate theinterface, as occur in known inserts.

Example 5

A substrate for a PCD compact was manufactured in the same way and usingthe same raw materials as the first substrate element of example 1,except that the height of the substrate was 13 millimetres. In otherwords, the whole substrate had substantially the same composition, shapeand diameter as the first substrate element described in example 1.

A first diamond layer formed of an unbonded aggregated mass of diamondgrains was deposited onto an end surface of the substrate, and a seconddiamond layer formed of an unbonded aggregated mass of diamond grainswas deposited onto the first layer to form an unbonded assembly. Thefirst diamond layer had a mean thickness of about 0.5 millimetres andthe second diamond layer had a mean thickness of about 2.5 millimetres,the first diamond layer being sandwiched between the substrate and thesecond diamond layer. The diamond grains of the first diamond layer hada fine-grain bi-modal distribution and the diamond grains of the seconddiamond layer had an ultra-fine-grain distribution. The diamond grainsof the second diamond layer had been coated with cobalt, whichconstituted 5 weight percent of the aggregated mass, and had then beensubjected to heat treatment in a hydrogen rich atmosphere at 850 degreescentigrade in order to terminate the surfaces with hydrogen.

The unbonded assembly was mounted within a capsule for an ultra-highpressure furnace, as is known in the art. The capsule was subjected to apressure of about 5.5 GPa and a temperature of about 1,400 degreescentigrade for a period of about 5 minutes. After sintering, the PCDcomposite compact was processed in the usual way to form an inserthaving a diameter of about 15.9 millimetres and a PCD structure withthickness in the range of about 2.2 millimetres.

The insert was analysed using scanning electron micrography (SEM).Particularly noteworthy was the absence of discernable pooling of cobaltbinder adjacent the interface between the PCD and the substrate. Thesample displayed an abrupt transition between the cemented carbide ofthe substrate and the PCD. In addition, no substantial exaggerateddiamond or WC grains were observed within the PCD layer proximate theinterface, as occur in known inserts.

Example 6

As example 2, except that the capsule was subjected to a pressure ofabout 6.8 GPa and a temperature of about 1,500 degrees centigrade for aperiod of about 5 minutes.

Although the foregoing description of consolidated superhard materials,production methods, and various applications of them contain manyspecifics, these should not be construed as limiting the scope of thepresent invention, but merely as providing illustrations of someexemplary embodiments. Similarly, other embodiments of the invention maybe devised which do not depart from the spirit or scope of the presentinvention. The scope of the invention is, therefore, indicated andlimited only by the appended claims and their legal equivalents, ratherthan by the foregoing description. All additions, deletions, andmodifications to the invention, as disclosed herein, which fall withinthe meaning and scope of the claims are to be embraced.

1. A polycrystalline diamond (PCD) composite compact element comprisinga PCD structure integrally bonded at an interface to a cemented carbidesubstrate; the PCD structure comprising coherently bonded diamond grainshaving a mean size no greater than about 15 microns; the cementedcarbide substrate comprising carbide particles dispersed in a metallicbinder, the carbide particles comprising a carbide compound of a metal;wherein the ratio of the amount of metallic binder to the amount of themetal at points in the substrate deviates from a mean value by at mostabout 20 percent of the mean value.
 2. A PCD composite compact elementaccording to claim 1, wherein the metal of the carbide particles is arefractory metal selected from the group consisting of W, Ti, Ta, andCr.
 3. A PCD composite compact element according to claim 1, wherein thesubstrate has a surface region extending from the interface to a depthof at least 1 mm, the region containing diamond particles dispersedwithin it.
 4. A PCD composite compact element according to claim 1,wherein the PCD structure comprises a first and a second region, themean size of the diamond grains of the first region being greater thanthe mean size of the diamond grains in the second region; the firstregion being proximate the substrate and the second region being remotefrom the substrate.
 5. A PCD composite compact element according toclaim 1, wherein the ratio of the amount of metallic binder to theamount carbon at points in the PCD structure deviates from a mean valueby at most 20 percent of the mean value, from the interface to a depthof at least 0.5 mm into the PCD structure.
 6. A method for making apolycrystalline diamond composite (PDC) compact element comprising apolycrystalline diamond (PCD) structure integrally bonded to a substrateformed of cemented carbide; the method including introducing a source ofexcess carbon to the substrate at or proximate a bonding surface of thesubstrate to form a carburised substrate or carburised substrateassembly; contacting an aggregated mass of diamond grains with thecarburised substrate or carburised substrate assembly adjacent orproximate the bonding surface to form an unbonded assembly; andsintering the diamond grains in the presence of a solvent/catalystmaterial for diamond at a temperature and pressure at which diamond isthermodynamically stable to form PCD; wherein the mean size of thediamond grains in the aggregated mass is no greater than about 30microns.
 7. A method according to claim 6, including introducing atleast 0.1 weight percent source of excess carbon to the substrate at orproximate the bonding surface of the substrate wherein the weightpercent is expressed as of the total substrate material within theregion in which the carbon is introduced.
 8. A method according to claim6, including forming the aggregated mass from diamond grains having amulti-modal size distribution.
 9. A method according to claim 6, whereinthe source of excess carbon is in the form of carbon black powder orgraphite.
 10. A method according to claim 6, including introducingdiamond to the substrate at or proximate the bonding surface of thesubstrate and converting at least some of the diamond into graphite toserve as a source of excess carbon.
 11. A method according to claim 6,including combining source of excess carbon in particulate or granularform with raw materials for the cemented carbide, forming thecombination into a substantially self-supporting green body, andsintering the green body at a pressure at which diamond is notthermodynamically stable.
 12. A method according to claim 6, includingcombining diamond grains with raw materials for cemented carbide,forming the combination into a substantially self-supporting green body;subjecting the green body to a temperature of at least 500 degreescentigrade and a pressure at which diamond is not thermodynamicallystable.
 13. A method according to claim 6, including introducingrefractory metal carbide particles into the aggregated mass of diamondgrains, the refractory metal carbide particles being selected from thegroup consisting of tungsten carbide, tantalum carbide, niobium carbideand vanadium carbide and/or introducing a refractory metal precursor formetal carbide into the aggregated mass of diamond grains, the refractorymetal being selected from the group consisting of tungsten, tantalum,niobium and vanadium in non-carbide compound or in elemental form.
 14. APCD cutter insert for a drill bit, the PCD cutter insert comprising aPCD composite compact element according to claim
 1. 15. A drill bit forboring into the earth comprising a PCD cutter insert according to claim14.